Abstract
When making judgments in a group, individuals often revise their initial beliefs about the best judgment to make given what others believe. Despite the ubiquity of this phenomenon, we know little about how the brain updates beliefs when integrating personal judgments (individual information) with those of others (social information). Here, we investigated the neurocomputational mechanisms of how we adapt our judgments to those made by groups of different sizes, in the context of jury decisions for a criminal. By testing different theoretical models, we showed that a social Bayesian inference model captured changes in judgments better than 2 other models. Our results showed that participants updated their beliefs by appropriately weighting individual and social sources of information according to their respective credibility. When investigating 2 fundamental computations of Bayesian inference, belief updates and credibility estimates of social information, we found that the dorsal anterior cingulate cortex (dACC) computed the level of belief updates, while the bilateral frontopolar cortex (FPC) was more engaged in individuals who assigned a greater credibility to the judgments of a larger group. Moreover, increased functional connectivity between these 2 brain regions reflected a greater influence of group size on the relative credibility of social information. These results provide a mechanistic understanding of the computational roles of the FPC-dACC network in steering judgment adaptation to a group’s opinion. Taken together, these findings provide a computational account of how the human brain integrates individual and social information for decision-making in groups.
Highlights
When making decisions in a group, individuals can adapt their initial beliefs according to the social influence produced by the opinions of other individuals in the group
When investigating 2 fundamental computations of Bayesian inference, belief updates and credibility estimates of social information, we found that the dorsal anterior cingulate cortex computed the level of belief updates, while the bilateral frontopolar cortex (FPC) was more engaged in individuals who assigned a greater credibility to the judgments of a larger group
The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Summary
When making decisions in a group, individuals can adapt their initial beliefs according to the social influence produced by the opinions of other individuals in the group In modern society, this type of process is widespread and can be seen in settings ranging from work meetings to the courtroom. To benefit from the opinion of others, the brain needs to track the likelihood that the group is making the most appropriate judgment [8] by estimating the credibility of social information [9,10,11]. Herding behavior in purchasing decisions [19,20] and collective animal behavior demonstrate a similar effect of group size on conformity [21,22] These examples indicate the importance of group size for social decision-making. Little is known about how the brain estimates the credibility of aggregate opinions of groups of different sizes
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